Errr, C2 and C4U have completely different "frames".
Every single part is rather different. Except the cores/screws, you really don't deviate much when it comes to those.
it doesnt help him alot if you don't tell him what the differences are...
And you helped more?
Lol, you don't even own the cubes yet, rofl.
The C4Y center is much more angular, and the cap resembles the newest model of C, or as some call it the C1.5, because of the tabs.
CII is completely different, because of the curvature, and the cap has a circular ridge. The center also has a notch, which resembles the retooled C to a degree. Apart from that, it's very different from the C.
The springs are an obvious difference.